F ADF Business Components Java EE Design Pattern Catalog

By using Oracle Application Development Framework (Oracle ADF) business components building-blocks and related design time extensions to JDeveloper, you get a prescriptive architecture for building richly functional and cleanly layered Java EE business services with great performance.

Table F-1 provides a brief overview of the numerous design patterns that the ADF Business Components layer implements for you. Some are the familiar patterns from Sun's Java EE BluePrints and some are design patterns that ADF Business Components adds to the list. For details about Java EE BluePrints, see the BluePrints page at the Oracle Technology Network web site at http://www.oracle.com/technetwork/java/index-jsp-136701.html.

Cleanly separates the roles of data and presentation, allowing multiple types of client displays to work with the same business information.

The ADF application module provides a generic implementation of a Model/View/Controller "application object" that simplifies exposing the application data model for any application or service, and facilitates declaratively specifying the boundaries of a logical unit of work. Additional UI-centric frameworks and tag libraries provided in JDeveloper help you implement the view and controller layers.

Interface / Implementation Separation

Cleanly separates the API or Interface for components from their implementation class.

ADF Business Components enforces a logical separation of client-tier accessible functionality (via interfaces) and its business tier implementation. JDeveloper handles the creation of custom interfaces and client proxy classes automatically.

Service Locator

Abstracts the technical details of locating a service so that the client can use it more easily.

ADF application modules are looked up using a simple configuration object which hides the low-level details of finding the service instance behind the scenes. For Fusion web applications, it also hides the implementation of the application module pool usage, a lightweight pool of service components that improves application scalability.

Inversion of Control

A containing component orchestrates the lifecycle of the components it contains, invoking specific methods that you can override at the appropriate times, so as to be able to focus more on what the code should do, instead of when it should be executed.

ADF components contain a number of easy-to-override methods that the framework invokes as needed during the course of application processing.

Dependency Injection

Simplifies application code, and increases configuration flexibility by deferring component configuration and assembly to the container.

ADF Business Components configures all its components from externalized XML metadata definition files. At runtime, the framework automatically injects dependent objects like view object instances into your application module service component and entity objects into your view rows, implementing lazy loading. It supports runtime factory substitution of components by any customized subclass of that component to simplify onsite application customization scenarios. Much of the ADF Business Components functionality is implemented via dynamic injection of validator and listener subscriptions that coordinate the framework interactions depending on what declarative features have been configured for each component in their XML metadata.

Active Record

Avoids the complexity of "anything to anything" object/relational mapping, by providing an object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.

ADF entity objects handle the database mapping functionality you use most frequently, including inheritance, association, and composition support, so you don't have to focus on object/relational mapping. They also provide a place to encapsulate both declarative business rules and one-off programmatic business domain.

ADF view objects automate the implementation of data access for reading data using SQL statements. ADF entity objects automate persistent storage of lightweight business entities. ADF view objects and entity objects cooperate to provide a sophisticated, performant data access objects layer, where any data queried through a view object can optionally be made fully updatable without requiring that you write any "application plumbing" code.

Session Facade

Prevents inefficient client access of entity beans and inadvertent exposure of sensitive business information by wrapping entity beans with a session bean.

ADF application modules are designed to implement a coarse-grained "service facade" architecture in any of their supported deployment modes. When deployed as EJB session beans or as a service interface, they provide an implementation of the Session Facade pattern automatically.

Value Object

Prevents unnecessary network roundtrips by creating one-off "transport" objects to group a set of related attributes needed by a client program.

ADF Business Components provides an implementation of a generic Row object, which is a metadata-driven container of any number and kind of attributes that need to be accessed by a client. The developer can work with the generic Row interface and do late-bound getAttribute("Price") and setAttribute("Quantity")calls, or optionally generate early-bound row interfaces like OverdueOrdersRow, to enable type-safe method calls like getPrice() and setQuantity(). Smarter than just a simple "bag 'o attributes", the ADF Row object can be introspected at runtime to describe the number, names, and types of the attributes in the row, enabling sophisticated, generic solutions to be implemented.

Page-by-Page Iterator

Prevents sending unnecessary data to the client by breaking a large collection into page-sized "chunks" for display.

ADF Business Components provides an implementation of a generic RowSet interface which manages result sets produced by executing view object SQL queries. The RowSet interface allows you to set a desired page size, for example 10 rows, and page up and down through the query results in these page-sized chunks. Since data is retrieved lazily, only data the user actually visits will ever be retrieved from the database on the backend, and in the client tier the number of rows in the page can be returned over the network in a single roundtrip.

Fast-Lane Reader

Prevents unnecessary overhead for read-only data by accessing JDBC APIs directly. This allows an application to retrieve only the attributes that need to be displayed, instead of finding all of the attributes by primary key when only a few are required by the client. Typically, implementations of this pattern sacrifice data consistency for performance, since queries performed at the raw JDBC level do not "see" pending changes made to business information represented by enterprise beans.

ADF view objects read data directly from the database for best performance; however, they give you a choice regarding data consistency. If updateability and/or consistency with pending changes is desired, you need only associate your view object with the appropriate entity objects whose business data is being presented. If consistency is not a concern, view objects can simply perform the query with no additional overhead. In either case, you never have to write JDBC data access code. You need only provide appropriate SQL statements in XML descriptors.

(Bean) Factory

Allows runtime instantiation and configuration of an appropriate subclass of a given interface or superclass based on externally configurable information.

Provides a restricted view of data and behavior of one or more business entities.

ADF view objects can surface any set of attributes and methods from any combination of one or more underlying entity objects to furnish the client with a single, logical value object to work with.

Value Messenger

Keeps client value object attributes in sync with the middle-tier business entity information that they represent in a bidirectional fashion.

The ADF Business Components value object implementation coordinates with a client-side value object cache to batch attribute changes to the EJB tier and receive batch attribute updates which occur as a result of middle-tier business logic. The ADF Value Messenger implementation is designed to not require any kind of asynchronous messaging to achieve this effect.

Continuations

Gives you the simplicity and productivity of a stateful programming model with the scalability of a stateless web solution.

ADF Business Components application module pooling and state management functionality combine to deliver this value-add. Application module pooling eliminates the need to dedicate application server tier resources to individual users and supports a "stateless with user affinity" optimization that you can tune.

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